15A-12 |
NMR spectroscopy and diffusion studies on processed cheese |
M. LI, Department of Food Science, North Carolina State University, Rm 129 Schaub Hall, Box 7624, Raleigh, NC 27695 and K. Keener. Processed cheeses are blends of natural cheeses, emulsifying salts, and other ingredients. Functional properties (melting and softening) of processed cheese are modified with heat and mechanical treatment. Nuclear magnetic resonance (NMR) is a non-invasive technique that can be used to evaluate the properties of processed cheese (e.g., quantify the amount of water and fat, describe the state of water, measure the fat particle size distribution, etc.). The objective of this research was to apply NMR spectroscopy and NMR Pulse Field Gradient (PFG) to quantify the water/fat ratio and fat distribution in processed cheeses. 2.0 mm x 2.0 mm x 4.00 cm cores were cut from three different cheeses samples: NCSU processed cheese, Land O'Lakes processed cheese and cheddar cheese, and placed in 5.0 mm diameter NMR tubes for measurement. NMR spectroscopy determined that the water/fat ratio (w/w) in these cheeses were 1.43:1 (NCSU processed cheese), 1.27:1 (Land O'Lakes processed cheese) and 1.16:1 (cheddar cheese), respectively. The water self-diffusion coefficients in these cheeses determined by NMR PFG technique are: 4.1x10-10 m2/s (NCSU processed cheese), 1.6 x10-10 m2/s (Land O'Lakes processed cheese) and 1.8 x10-10 m2/s (Cheddar cheese). The fat diffusion coefficients in these cheeses are 3.3 x10-12 m2/s (Land O'Lakes processed cheese) and 4.6 x10-12 m2/s (Cheddar cheese). The fat diffusion coefficient in the NCSU processed cheese was non-detectable. Fat distribution (mean fat droplet radius +/- standard deviation) was calculated for Land O'Lakes processed cheese (1855 nm +/- 834 nm) and Cheddar cheese (2186 nm +/- 2015 nm). These results show that fat droplet size in processed cheese (Land O'Lakes) was more uniform than the cheddar cheese. This technique can non-invasively measure water/fat ratio and fat droplet size in processed cheese. This method can provide useful data in formulating and mixing of processed cheese.
Session 15A, Dairy Foods
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